Answer to Question 1
The first species to reinvade a disturbed environment are called opportunists or pioneer species. They tend to be fast growing, rapidly reproducing, environmentally tolerant species that can spread across the disturbed area quickly. In colonizing a previously disturbed area, these organisms tend to begin the process of repair, improving the soil or modifying the local climate in ways that can result in their replacement by other, slower growing organisms that ultimately have competitive advantages. In general, succession patterns are predictable, at least in terms of the types of plants that will become prevalent at various stages of succession. If many species are equally well suited to the environmental conditions at a particular stage of succession, however, an element of unpredictability may be introduced into the succession pattern. Thus a diversity of outcomes is possible, and this diversity may be reflected in the biodiversity of a region subject to disturbance. Indeed, we will see in the next section that a modest level of disturbance may be required for high-diversity ecosystems to become established. Succession is one indication that the biosphere has the capacity to heal, that it is resilient to perturbation.
Answer to Question 2
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The structure of a typical flower.
A cutaway of a typical water pump showing the long bearing assembly and the seal. The weep hole is ...
A typical hand-operated vacuum pump.
Typical joint changes associated with osteoarthritis.
Trees provide ecosystem services to people
Annotation of a DNA sequence containing part of the human beta-globin gene